Lipids

Question 1

Hydrolytic Rancidity: main chemical reaction (type)?

Answer 1

Hydrolysis of the ester bond between glycerol and fatty acid

Note: the oxidation state is not affected

Question 2

Hydrolytic Rancidity: What are the products?

Answer 2

Glycerol and free fatty acids

Question 3

Hydrolytic Rancidity: what speeds up the process?

Answer 3

Heat, water content, lipases

Question 4

Hydrolytic Rancidity: What foods are particularly affected (and why)?

Answer 4

Foods that undergo frying and foods with high lipase activity

Question 5

Oxidative Rancidity: main chemical reaction (type)?

Answer 5

Hydrogen abstraction from a CH2 group next to or, if available, in between DBs on a FA, followed by attachment of O2. Overall, the lipid is oxidized

Question 6

Oxidative Rancidity: What are the products?

Answer 6

1. Hydroperoxides

2. Mostly ketones and aldehydes from ROOH decomposition

Question 7

Oxidative Rancidity: What speeds up the process?

Answer 7

Heat, light, redox-active metal ions, lipoxygenases

Question 8

Oxidative Rancidity: What foods are particularly affected (and why)?

Answer 8

Foods that contain PUFAs, because the CH2 group in between DBs is attacked preferentially

Question 9

Antioxidant Properties of Citric Acid

Answer 9

Citric acid is a metal chelator, and prevents redox reactive metals such as Fe and Cu from initiating or promoting lipid oxidation

Question 10

Antioxidant Properties of BHT

Answer 10

BHT is a phenolic radical scavenger. It forms
resonance-stabilized radicals that do not attack fatty
acids, but rather recombine with other radicals

Question 11

Diacylglycerols are less polar than monoacylglycerols

T/F

Answer 11

True

Monoacylglycerols are the most polar simple lipid

Question 12

Butanoic acid is more polar than palmitic acid

T/F

Answer 12

True
Butanoic acid is a short chain saturated fatty acid and has partial solubility in water. This is because it is more polar than the palmitic (LCFA) that is practically insoluble in water

Question 13

α-linolenic acid is more unsaturated than γ-linolenic acid T/F

Answer 13

False

They have the same amount of saturation (3 DB)

Question 14

α-linolenic acid is essential while stearic acid is not

T/F

Answer 14

True

α-linolenic acid is one of the 2 essential FA

Question 15

The shorthand notations 18:1 ω9 and 18:1 ∆9 describe the same fatty acid T/F

Answer 15

True

They both describe oleic acid

Question 16

Which of the following conditions do not accelerate lipid oxidation
A. Light
B. Moisture levels below the monolayer
C. Moisture levels at the monolayer
D. Temperature
E. Presence of Fe2+
F. Presence of Ca2+

Answer 16

B,C,F

Question 17

Rank the following fatty acids in terms of increasing melting point
A. Linoleic acid
B. Oleic acid
C. Myristic acid (C14:0)
D. Stearic acid
E. Arachidic acid (C20:0)
F. Docosahexaenoic acid

Answer 17

Lowest to highest BP

F,A,B,C,D,E